Malaria is one of the world's most prevalent serious infectious diseases, with approximately 250 million cases and 1 million deaths per year (WHO, 2009). Mortality is primarily in children under the age of five and in pregnant women. Every 45 seconds, an African child dies of malaria. The disease is transmitted from person to person by infected mosquitoes, so past eradication efforts involved massive insecticide campaigns. These were successful in the Southeast U.S. for example, but failed in most poorly developed tropical countries. Current efforts involve distribution of bednets, particularly bednets impregnated with insecticide, to prevent mosquito bites at night. However, resistance to insecticides and to anti-malarial drugs for both prevention and treatment is rapidly rising. Thus, the need for a malaria vaccine is imperative for protection of millions of people from disease (http://www.globalvaccines.org/content/malaria+vaccine+program/19614).
Malaria caused by Plasmodium falciparum remains a major public health threat, especially among children and pregnant women in Africa. An effective malaria vaccine would be a valuable tool to reduce the disease burden and could contribute to elimination of malaria in some regions of the world. Current malaria vaccine candidates are directed against human and mosquito stages of the parasite life cycle, but thus far, relatively few proteins have been studied for potential vaccine development.
The most advanced vaccine candidate, RTS,S, conferred partial protection against malaria in phase II clinical trials and is currently being evaluated in a phase III trial in Africa. (The Journal of Clinical Investigation 120(12) 4168-4178, 2010).
The CSP is the predominant surface antigen on sporozoites. CSP is composed of an N-terminal region that binds heparin sulfate proteoglycans (RI), a central region containing a four-amino-acid (NPNA) repeat, and a GPI-anchored C-terminal region containing a thrombospondin-like domain (RII). The region of the CSP included in the RTS,S vaccine includes the last 16 NPNA repeats and the entire flanking C-terminus. HBsAg particles serve as the matrix carrier for RTS,S, 25% of which is fused to the CSP segment (The Journal of Clinical Investigation 120(12) 4168-4178, 2010).
In a series of phase II clinical trials for RTS,S, 30%-50% of malaria-naive adults immunized with RTS,S were protected against challenge by mosquitoes infected with the homologous P. falciparum clone. In phase II field trials in the Gambia and Kenya, RTS,S conferred short-lived protection against malaria infection in approximately 35% of adults, although results from the Kenya trial did not reach statistical significance. Approximately 30%-50% of children and infants immunized with RTS,S in phase II trials conducted in Mozambique, Tanzania, and Kenya were protected from clinical malaria, however, protection was generally short-lived (The Journal of Clinical Investigation 120(12) 4168-4178, 2010). Results from a pivotal, large-scale Phase III trial, published Nov. 9, 2012, online in the New England Journal of Medicine (NEJM), show that the RTS,S malaria vaccine candidate can help protect African infants against malaria. When compared to immunization with a control vaccine, infants (aged 6-12 weeks at first vaccination) vaccinated with RTS,S had one-third fewer episodes of both clinical and severe malaria and had similar reactions to the injection.
There are currently no licensed vaccines against malaria. Highly effective malaria vaccine is strongly desired.
Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome, potentially yielding safer and cheaper vaccine candidates. A handful of prophylactic VLP-based vaccines is currently commercialized worldwide: GlaxoSmithKline's Engerix® (hepatitis B virus) and Cervarix® (human papillomavirus), and Merck and Co., Inc.'s Recombivax HB® (hepatitis B virus) and Gardasile (human papillomavirus) are some examples. Other VLP-based vaccine candidates are in clinical trials or undergoing preclinical evaluation, such as, influenza virus, parvovirus, Norwalk and various chimeric VLPs. Many others are still restricted to small-scale fundamental research, despite their success in preclinical tests. The implications of large-scale VLP production are discussed in the context of process control, monitorization and optimization. The main up- and down-stream technical challenges are identified and discussed accordingly. Successful VLP-based vaccine blockbusters are briefly presented concomitantly with the latest results from clinical trials and the recent developments in chimeric VLP-based technology for either therapeutic or prophylactic vaccination (Expert Rev. Vaccines 9(10), 1149-1176, 2010).
Chikungunya virus (CHIKV) has infected millions of people in Africa, Europe and Asia since this alphavirus reemerged from Kenya in 2004. The severity of the disease and the spread of this epidemic virus present a serious public health threat in the absence of vaccines or antiviral therapies. It is reported that a VLP vaccine for epidemic Chikungunya virus protects non-human primates against infection (Nat Med. 2010 March; 16(3): 334-338). US patent publication No. 2012/0003266 discloses a virus-like particle (VLP) comprising one or more Chikungunya virus structural polypeptides which is useful for formulating a vaccine or antigenic composition for Chikungunya that induces immunity to an infection or at least one symptom thereof. WO2012/106356 discloses modified alphavirus or flavivirus virus-like particles (VLPs) and methods for enhancing production of modified VLPs for use in the prevention or treatment of alphavirus and flavivirus-mediated diseases. (these cited references are herein incorporated by reference).